1. Field of the Invention
The present invention relates to adsorbent canisters for temporarily trapping fuel vapor (e.g., gasoline vapor) vaporized in a fuel tank.
2. Description of the Related Art
Gas vehicle such as automobile is equipped with an adsorbent canister as a part of a fuel vapor processing system for processing fuel vapor vaporized in a fuel tank. The adsorbent canister has a hollow casing and an adsorbent filled in the casing. The casing has a fuel introducing port for introducing the fuel vapor from the fuel tank into the casing, and an air communicating port for introducing ambient air into the casing. The adsorbent is composed of activated carbon or the like and can adsorb and desorb the fuel vapor. That is, the fuel vapor flows into the adsorbent canister and adsorbs onto the adsorbent, e.g., during parking, and desorbs from the adsorbent due to purge operation while the engine is running.
Because a part of the fuel vapor adsorbing onto the adsorbent desorbs from the adsorbent and diffuses in the casing with time, there is a risk that the fuel vapor flows out of the adsorbent canister through the air communicating port. Accordingly, some conventional adsorbent canisters have a casing provided with a partition configured to divide an inner space of the casing into a first adsorption chamber closed to the fuel introducing port and a second adsorption chamber closed to the air communicating port. The fuel vapor flowing into the casing via the fuel introducing port is trapped in the first adsorption chamber, and a part of the fuel vapor diffusively flowing out of the first adsorption chamber is trapped in the second adsorption chamber.
Japanese Laid-Open Patent Publication No. H09-21361 discloses an adsorbent canister having a communicating chamber connected to the first adsorption chamber and the second adsorption chamber and having partition walls therein. The partition walls define a meandering path in the communicating chamber such that the length of a pathway between the first adsorption chamber and the second adsorption chamber is increased. This configuration may require a longer period of time for the fuel vapor to reach the second adsorption chamber from the first adsorption chamber, so that the adsorbent canister can decrease the amount of the fuel vapor diffusively flowing into the second adsorption chamber from the first adsorption chamber in a certain period of time. Consequently, it is able to reduce the amount of the fuel vapor diffusively flowing into the atmosphere during parking.
Japanese Laid-Open Patent Publication No. 2005-23835 discloses an adsorbent canister equipped with a cartridge having a labyrinth structure. The labyrinth structure requires a longer period of time for the fuel vapor to pass through the cartridge, so that it is able to reduce the amount of the fuel vapor passing through the cartridge in a certain period of time. Consequently, it is able to reduce the amount of the fuel vapor flowing into the atmosphere during parking.
In these adsorbent canisters, the pathway between the first adsorption chamber and the second adsorption chamber is lengthened, however the total volume of the pathway is not increased. Therefore, there has been a need in the art for an improved adsorbent canister.